All of these rewards can be achieved without spending any credits, and so are free if you want them to be. If you don't want to play with starter balls, or free leftover balls from your bag, or you don't want to play for them at all, that's up to you.
the average Joe player on here isn’t thinking to change his balls prior to going after a daily or weekly goal.
You both are correct, IMO.
Most members, myself included, will just use the balls they use. Odds are more will than not. WGT banks on the odds.
Some of the goals, and achievements are based upon score, birdies, eagles, coin room wins, etc... Unlike Mr. Mags, et al, we lesser players are at a disadvantage with rocks. WGT knows this. G & A has a symbiotic relationship with the general membership, we get a little back while they get increased play, and revenues from balls hits. A win-win LOL
EDIT: And, next time we play an alt match, on Kiawah, and I drive over the 3 par green, into unknown pond, I will finally earn that achievement and get some XP.